Port fuel direct injection (PFDI) engines include both port injection and direct injection of fuel and may advantageously utilize each injection mode. For example, at higher engine loads, fuel may be injected into the engine using direct fuel injection for improved engine performance (e.g., by increasing available torque and fuel economy). At lower engine loads and during engine starting, fuel may be injected into the engine using port fuel injection to provide improved fuel vaporization for enhanced mixing and to reduce engine emissions. Further, port fuel injection may provide an improvement in fuel economy over direct injection at lower engine loads. The enhanced fuel economy may be ascribed to a reduction in pumping work due to a higher manifold pressure (via fuel vapor pressure) and a more complete combustion due to better mixing of fuel and air. Further still, noise, vibration, and harshness (NVH) may be reduced when operating with port injection of fuel. In addition, both port injectors and direct injectors may be operated together under some conditions to leverage advantages of both types of fuel delivery or in some instances, differing fuels.
In PFDI engines, a lift pump (also termed, low pressure pump) supplies fuel from a fuel tank to both port fuel injectors and a direct injection fuel pump. The direction injection fuel pump may supply fuel at a higher pressure to direct injectors. The direct injection (DI) fuel pump may not be activated during certain periods of engine operation (e.g., during port fuel injection at low engine loads) which may affect lubrication of the DI fuel pump and increase wear, NVH, and degradation of the DI fuel pump. To reduce DI fuel pump degradation and improve lubrication, PFDI engines may continue direct injecting fuel at engine idle conditions. However, this operation can result in excessive NVH from ticks generated by actuation of a solenoid activated check valve in the DI fuel pump. These ticks may be audible to a vehicle operator and passengers due to a lack of engine noise to mask the DI fuel pump noise during idling conditions. To counter ticking noises during idling, the DI fuel pump may be operated in a default pressure mode by deactivating the solenoid activated check valve. Additionally, pump pressure and fuel rail pressure may be mechanically regulated, during lower engine loads, in the default pressure mode.
The DI fuel pump may be operated in two distinct, albeit, potentially overlapping, modes: the default pressure mode and a variable pressure mode. As such, the solenoid activated check valve may be activated in the variable pressure mode and may be deactivated in the default pressure mode.
The DI fuel pump may function as a pressure regulator and may continually regulate fuel rail pressure in a high pressure fuel rail, whether the solenoid activated check valve is in a deactivated or activated condition. Herein, the DI fuel pump may regulate fuel pressure in the high pressure fuel rail by adding fuel to the high pressure fuel rail if the fuel rail pressure is below a predetermined threshold. When the fuel rail pressure is above the predetermined threshold, this pressure regulation feature of the DI fuel pump may be inactive. As such, the control of fuel rail pressure may be entirely mechanical-hydraulic in nature.
When the solenoid activated check valve is activated, the DI fuel pump may function as a fuel volume regulator. The fuel volume regulator feature in the DI fuel pump may add a given volume of fuel to the high pressure fuel rail depending on a command from a controller sent to the solenoid activated check valve. Normally, this command may be based on a comparison of a reading from a fuel rail pressure sensor to a desired fuel rail pressure. Nonetheless, the DI fuel pump mechanism may effectively regulate fuel volume when the solenoid activated check valve is activated. Accordingly, the DI fuel pump may also be termed a fuel volume metering device.
The inventors herein have recognized potential issues with controlling lift pump operation. For example, lift pump operation may be based on a comparison between an actual (or observed) and expected DI fuel pump volumetric efficiency. However, this approach to lift pump control may only be suitable when the DI fuel pump is functioning as a fuel volume metering device. In other words, a method of lift pump control used during the variable pressure mode of the DI fuel pump may not be suitable for default pressure mode operation of the DI fuel pump.
In another example, during default pressure mode operation of the DI fuel pump, the low pressure pump may be operated continuously. As such, conventional methods of controlling the low pressure pump during the default pressure mode expend excessive pump power, thereby reducing fuel economy and pump durability. Further, operational and maintenance costs of the lift pump may be increased.
The inventors herein have recognized the above issues and identified an approach to at least partly address the above issues. In one example approach a method of operating a low pressure pump is provided. The method comprises, when operating a high pressure pump in a default pressure mode, pulsing a low pressure pump when pressure in a high pressure fuel rail decreases below a threshold, and when operating the high pressure pump in a variable pressure mode, pulsing the low pressure pump based on presence of fuel vapor at an inlet of the high pressure pump. In this way, the low pressure pump is actuated only when certain conditions prevail, reducing energy consumption.
For example, a DI fuel pump of a fuel system in a PFDI engine may be operated in one of two modes: a default pressure mode and a variable pressure mode. An electronically controlled solenoid activated inlet check valve may be activated, and maintained active, during the variable pressure mode. In the default pressure mode, the electronically controlled solenoid activated inlet check valve may be deactivated and the DI fuel pump may be operated with a constant default pressure. As such, a pressure relief valve may regulate pressure in a compression chamber of the DI fuel pump to a default pressure based on a setting of the pressure relief valve. Further, pressure in a fuel rail coupled to the DI fuel pump may be monitored by a pressure sensor. As such, low pressure pump operation may be controlled based on readings from the pressure sensor. In addition, low pressure pump operation during the default pressure mode of the DI fuel pump may be particularly based on pressure readings learned during one or more compression strokes in the DI fuel pump. Accordingly, when the DI fuel pump is operating in default pressure mode and pressure in the fuel rail during one or more compression strokes drops below a threshold, the low pressure pump may be pulsed at full voltage to increase pressure in the fuel rail. Alternatively, the low pressure pump may be pulsed for a specific time duration.
When the DI fuel pump is operating in variable pressure mode, the lift pump may be pulsed based on presence of fuel vapor at an inlet of the DI fuel pump. Fuel vapor may be sensed when a compression stroke in the DI fuel pump does not cause an expected corresponding increase in pressure in the fuel rail. In response to the detection of vapor at DI fuel pump inlet, the lift pump may be pulsed at full voltage to increase fuel rail pressure.
In this way, lift pump operation may be controlled for multiple benefits. The lift pump may be pulsed at full voltage or for short predetermined durations to enable a faster increase in fuel rail pressure. By actuating the lift pump only under certain conditions, lift pump energy consumption may be reduced leading to an increase in fuel economy which in turn can ease operating expenses. Further, durability of the lift pump may be extended, and maintenance costs of the lift pump may be decreased. Overall, operation of the lift pump may be improved and more efficient.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.